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1.
We present results from a 484 km wide-angle seismic profile acquired in the northwest part of the South China Sea (SCS) during OBS2006 cruise. The line that runs along a previously acquired multi-channel seismic line (SO49-18) crosses the continental slope of the northern margin, the Northwest Subbasin (NWSB) of the South China Sea, the Zhongsha Massif and partly the oceanic basin of the South China Sea. Seismic sections recorded on 13 ocean-bottom seismometers were used to identify refracted phases from the crustal layer and also reflected phases from the crust-mantle boundary (Moho). Inversion of the traveltimes using a simple start model reveals crustal images in the study area. The velocity model shows that crustal thickness below the continental slope is between 14 and 23 km. The continental part of the line is characterized by gentle landward mantle uplift and an abrupt oceanward one. The velocities in the lower crust do not exceed 6.9 km/s. With the new data we can exclude a high-velocity lower crustal body (velocities above 7.0 km/s) at the location of the line. We conclude that this part of the South China Sea margin developed by a magma-poor rifting. Both, the NWSB and the Southwest Sub-basin (SWSB) reveal velocities typical for oceanic crust with crustal thickness between 5 and 7 km. The Zhongsha Massif in between is extremely stretched with only 6–10 km continental crust left. Crustal velocity is below 6.5 km/s; possibly indicating the absence of the lower crust. Multi-channel seismic profile shows that the Yitongansha Uplift in the slope area and the Zhongsha Massif are only mildly deformed. We considered them as rigid continent blocks which acted as rift shoulders of the main rift subsequently resulting in the formation of the Northwest Sub-basin. The extension was mainly accommodated by a ductile lower crustal flows, which might have been extremely attenuated and flow into the oceanic basin during the spreading stage. We compared the crustal structures along the northern margin and found an east-west thicken trend of the crust below the continent slope. This might be contributed by the east-west sea-floor spreading along the continental margin. 相似文献
2.
Based on two-dimensional gravity modeling, the density section of the lithosphere beneath Taiwan and the surrounding areas is constructed. According to the density parameters, the lithosphere of this region comprises both the continental and oceanic types. The continental lithosphere is lighter than the oceanic one and demonstrates insignificant density differentiation through the entire section. The oceanic lithosphere is more contrasting with respect of both the crust and mantle density. The complicated Taiwan density structure corresponding to Taiwan Island is defined to be superimposed on the transition zone between the continental and oceanic lithospheric blocks. This structure with contrasting density boundaries is characterized by the elevated and high density values of its constituting heterogeneities. The formation of the Taiwan density structure is related to geodynamic processes in the Taiwan area marking the collision zone between the Eurasian and Philippine Sea plates. 相似文献
3.
洋-陆过渡带是理解大陆岩石圈破裂和海底初始扩张的关键位置,但是在南海北部地区仍然存在关于相关地质过程的诸多疑问.通过近年开展的国际大洋发现计划航次以及深部地质地球物理探测,取得以下4个方面的认识.（1）南海北部的洋-陆边界一般与自由空间重力异常的正-负值过渡位置对应,而更加准确地限定需要结合反射、折射地震资料.稳定大洋岩石圈生成与大陆岩石圈最终破裂之间的洋-陆过渡边界的位置比以往认为的还应往深海盆方向移动.（2）洋-陆过渡带代表了远端带构造作用减弱和岩浆作用逐渐增强的区域.陆坡地壳发育扩张后岩浆底侵、洋-陆过渡带发育同破裂期岩浆喷出结构和侵入反射体.（3）在中生代的古俯冲带弧前区域,新生代的断裂沿着早期的构造开始活动,岩石圈多处发生强烈的共轭韧性剪切作用.随着大陆岩石圈的进一步拉伸减薄,部分靠陆一侧的裂谷中心停止张裂,成为夭折裂谷,以台西南盆地南部凹陷、白云凹陷、西沙海槽为代表,而南海陆缘异常伸展和最终破裂的地方集中在南侧裂谷中心.夭折裂谷下亦发现地幔蛇纹石化,进一步反映了较弱的同破裂岩浆活动.（4）南海初始洋壳的增生沿着大陆边缘走向具有显著的变化,南海东北部洋-陆过渡带下伏地幔明显抬升和部分蛇纹石化,地震纵、横波速度以及折射波衰减特征都支持此观点,反映南海东北部是一个贫岩浆型大陆边缘.未来,南海北部洋-陆过渡带有望成为南海“莫霍钻”的理想备选钻探区. 相似文献
4.
利用最新多道地震剖面资料,结合重力、磁力、地形等地球物理资料,揭示了中沙地块南部断裂空间展布特征、断裂发育时期、断裂内部构造形变特征及深部地壳结构,并基于认识探讨了断裂的发育机制。研究结果认为,中沙地块南部陆缘构造属性为非火山型被动大陆边缘：地壳性质从西北向东南由减薄陆壳向洋陆过渡壳再向正常洋壳发育变化;Moho面埋深从中沙地块下方的26 km快速抬升到海盆的10~12 km;从中沙地块陡坡至其前缘海域的重力异常明显负异常区为洋陆过渡带,在重力由高值负异常上升到海盆的低值正、负异常的边界为洋陆边界。中沙地块南部发育有4组阶梯状向海倾的深大正断裂,主要发育时期为晚渐新世到中中新世。断裂早期发育与南海东部次海盆近NS向扩张有关,后期遭受挤压变形、与菲律宾海板块向南海的NWW向仰冲有关。该研究有助于更好认识南海海盆的扩张历史和南海被动大陆边缘的类型。 相似文献
5.
被动陆缘洋陆转换带和岩石圈伸展破裂过程分析及其对南海陆缘深水盆地研究的启示 总被引：2，自引：0，他引：2
作为伸展陆壳和正常洋壳之间重要的过渡和衔接,洋陆转换带(ocean-continent transition,简写为OCT)蕴含有丰富的地壳岩石圈伸展破裂过程的信息。文中通过系统的资料调研,在总结OCT研究历史、现状和发展趋势的基础上,阐明了OCT的现代概念、类型及其识别标志;详细介绍了以OCT为基础而建立的被动陆缘地壳岩石圈结构构造单元划分方案、表层沉积盆地构造地层格架及重要的构造变革界面特征;分析了大型拆离断层在地壳岩石圈薄化、地幔剥露过程中的控制作用;揭示了陆缘变形集中、迁移和叠合的规律,建立了被动陆缘岩石圈伸展、薄化、剥露和裂解模式。最后,论文对比了国际非岩浆型被动大陆边缘与我国南海OCT的研究,介绍了南海OCT和陆缘深水超深水盆地研究的新发现,提出深入研究南海OCT将为南海陆缘构造演化、洋盆扩张过程和深水超深水盆地的成因机制研究提供新的启示。 相似文献
6.
对南海南部地壳结构研究有助于揭示南海完整的演化历史。本研究对南海南部获取的两条多道地震剖面进行了地震 解释,并对重力数据进行了壳幔密度反演。其中 NH973-1 测线始于南海西南次海盆,覆盖了南沙中部的北段;NH973-2 测 线始于南海东部次海盆,穿越礼乐滩东侧。反演结果显示,莫霍面埋深在海盆区 10~11 km,陆缘区 15~21 km 左右,洋壳向 陆壳莫霍面深度迅速增加。海盆区厚度在 6~7 km,为典型的洋壳;陆缘区地壳厚度在 15~19 km,为减薄型地壳。进一步研 究表明(1)在西南次海盆残余扩张脊之下,莫霍面比两侧略深;(2)在礼乐滩外侧海盆区有高值重力异常体,推测为洋壳与深 部岩浆混合的块体;(3)南沙区域上地壳存在高密度带,且横向上岩性可能变化。南海南部陆缘未发现有下地壳高速层,有 比较一致的构造属性和拉张样式,为非火山型陆缘。我们对两条测线陆缘的伸展因子进行了计算,发现上地壳脆性拉伸因 子与全地壳拉伸因子存在差异,其陆缘的拉张模式在纵向上是不均匀一的。 相似文献
7.
南海的形成和演化得到了广泛研究,前人提出了超过5种成因模式,当前流行是海底扩张模式,但它难以合理解释南海洋壳上的洋中脊跳跃和南海中央海盆上的大陆残片。本文首先基于南海中央海盆中的两条高精度地震勘探剖面,在深入剖析洋壳的分层结构基础上,对这两条地震勘探剖面进行了新的构造地质解释。然后通过伸展构造的形成过程,发展了地幔上涌和陆壳重力滑移双驱动大陆漂移模型,最后深入研究了南海的形成和演化过程。结果说明,南海的形成是一种“构造挤出+主动漂移”模式。构造挤出是印度-欧亚大陆碰撞造成的欧亚东南缘微陆块大规模被动挤出,而主动漂移是微陆块在被挤出后发生了主动裂解漂移。南海中央海盆上残留的地震反射特征,是微陆块主动漂移后造成的海底被扩张现象。并进一步恢复了南海演化过程中周边陆块的运动演化历史。所提出的新模式能够合理解释南海的洋中脊跳跃现象及大陆残片的成因机制。新大陆漂移模型为板块运动提供了一个新的动力模式。 相似文献
8.
利用中国地震台网和ISC台站记录的P波到时数据,采用球坐标系有限差分地震层析成像方法反演了南海东北部及其邻近地区壳幔三维P波速度结构,并分析了不同地质单元的构造差异及其深部特征。结果表明:南海东北部表现出陆架地区的岩石层特性,属于华南大陆向海区的延伸,岩石层厚度较大,现今不存在大规模的地幔热流活动,推测大陆边缘张裂作用仅限于地壳内部而没有延伸进入上地幔,具有非火山型大陆边缘的深部特点。中央海盆附近上地幔P波速度明显降低,与海盆下方地幔热流活动密切相关。不同的速度异常特征表明:华南大陆暨台湾地区属于欧亚大陆的正常地壳或是与菲律宾海板块相互作用产生的增厚型地壳,冲绳海槽则是弧后扩张产生的减薄型地壳。滨海断裂带作为华南大陆高速异常和南海北部高速异常的分界,代表了一定地质时期华南地块和南海地块的拼合边界。断裂附近的上地幔低速异常揭示了闽粤沿海岩浆作用的深层动力机制。吕宋岛弧、马尼拉海沟、东吕宋海槽的速度异常与其所处的特殊构造位置有密切的关系,清晰地反映出岛弧俯冲带的地壳结构差异;台湾南部至吕宋岛弧的上地幔低速异常揭示了两个重要火山链的深部构造特征,北吕宋海脊下方100 km深度的条带状高速异常有可能代表了俯冲下沉的岩石层板片。 相似文献
9.
中国边缘海域及其邻区的岩石层结构与构造分析 总被引：3，自引：0，他引：3
利用中国边缘海域近年的地震层析成像结果,根据速度异常和各向异性分析东海、黄海和南海北部的岩石层结构和构造,讨论中朝块体和扬子块体在黄海内部的拼合边界(黄海东部断裂带)、东海陆架盆地上地幔异常与岩石层形成演化、南海北部地壳底部高速层的成因及地幔活动等问题。分析表明,黄海东部与朝鲜半岛之间存在一个深部构造界限(大致对应于黄海东部断裂带),分界两侧Pn波速度各向异性存在明显差异,反映不同构造应力和断裂剪切运动作用下的岩石层地幔变形特征。东海陆架下方的低速异常揭示了张裂盆地形成时期的地幔活动痕迹,表明中、新生代期间发生过地幔上涌并造成岩石层减薄,菲律宾海板块向西俯冲引发的地幔活动对东海陆架岩石层的形成、演化产生明显的影响。南海北部岩石层厚度较大并且温度相对偏低,地幔异常仅限于局部地区,估计南海北部大陆边缘的地壳底部高速层形成于张裂发生之前,或者是地壳形成时期壳幔分异时的产物。南海中央海盆的扩张不仅导致地壳拉张,软流层物质上涌,而且也造成岩石层地幔减薄甚至缺失。 相似文献
10.
《Gondwana Research》2016,29(4):1329-1343
Continental rifting to seafloor spreading is a continuous process, and rifting history influences the following spreading process. However, the complete process is scarcely simulated. Using 3D thermo-mechanical coupled visco-plastic numerical models, we investigate the complete extension process and the inheritance of continental rifting in oceanic spreading. Our modeling results show that the initial continental lithosphere rheological coupling/decoupling at the Moho affects oceanic spreading in two manners: (1) coupled model (a strong lower crust mechanically couples upper crust and upper mantle lithosphere) generates large lithospheric shear zones and fast rifting, which promotes symmetric oceanic accretion (i.e. oceanic crust growth) and leads to a relatively straight oceanic ridge, while (2) decoupled model (a weak ductile lower crust mechanically decouples upper crust and upper mantle lithosphere) generates separate crustal and mantle shear zones and favors asymmetric oceanic accretion involving development of active detachment faults with 3D features. Complex ridge geometries (e.g. overlapping ridge segments and curved ridges) are generated in the decoupled models. Two types of detachment faults termed continental and oceanic detachment faults are established in the coupled and decoupled models, respectively. Continental detachment faults are generated through rotation of high angle normal faults during rifting, and terminated by magmatism during continental breakup. Oceanic detachment faults form in oceanic crust in the late rifting–early spreading stage, and dominates asymmetric oceanic accretion. The life cycle of oceanic detachment faults has been revealed in this study. 相似文献
11.
Yanghui Zhao Shaoru Yin Jiabiao Li Jie Zhang Hanghang Ding 《International Geology Review》2020,62(7-8):955-969
ABSTRACT The volume of seamounts is an essential indicator of the intensity of mantle convection during the evolution of the oceanic lithosphere. Drilling and dredging samples suggest volcanic seamounts are widely distributed in the oceanic basin of the South China Sea, and most of them were formed after cessation of seafloor spreading. By using an SRTM15_PLUS Digital Elevation Model with a 15-arc-second grid, we developed a spatial filtering method based on the Top Hat Transform to extract seamounts. With a combined analysis of basalt dating results from previous studies and gravity anomaly data, an accurate estimation of seamount volume and its spatiotemporal distribution have been obtained. In addition to an asymmetric distribution of the seamounts with a larger volume in the northern flank, clusters of seamounts can be observed at certain locations in the abyssal plain. Due to the consistency between the distribution of the seamount volume and the seafloor spreading features in the South China Sea basin, we propose the ridge jump may induce additional partial melting zones which account for the larger number of seamounts developed in the northern flank while the re-orientation of the extension during seafloor spreading dominated the distribution of post-spreading magmatism. Similar to other marginal basins, magmas formed by spontaneous partial melting would migrate through weak lithosphere where the extension direction changed, resulting in post-spreading magmatism in those lithospheric weak zones. 相似文献
12.
本篇讨论大陆岩石圈拆沉、伸展与裂解作用过程。由于大陆岩石圈厚度大而且很不均匀,产生裂谷的机制比较复杂。大陆碰撞远程效应的触发,岩石圈拆沉,以及板块运动的不规则性和地球应力场方向转折,都可能产生岩石圈断裂和大陆裂谷。岩石圈拆沉为在重力作用下"去陆根"的作用过程,演化过程可分为大陆根拆离、地壳伸展和岩石圈地幔整体破裂三个阶段。大陆碰撞带、俯冲的大陆和大洋板块、克拉通区域岩石圈,都可能产生岩石圈拆沉。大陆岩石圈调查表明,拉张区可见地壳伸展、岩石圈拆离、软流圈上拱和热沉降;它们是大陆岩石圈伸展与裂解早期的主要表现。从初始拉张的盆岭省到成熟的张裂省,拆离后地壳伸展成复式地堑,下地壳幔源玄武岩浆侵位,断裂带贯通并切穿整个岩石圈,表明地壳伸展进入成熟阶段。中国东北松辽盆地和西欧北海盆地曾处于成熟的张裂省。岩石圈破裂为岩浆侵位提供了阻力很小的通道网。岩浆侵位作用伴随岩石圈破裂和热流体上涌,成熟的张裂省可发展成大陆裂谷。多数的大陆裂谷带并没有发展成威尔逊裂谷带和洋中脊,普通的大陆裂谷要演化为威尔逊裂谷带,必须有来自软流圈的长期和持续的热流和玄武质岩浆的供应。威尔逊裂谷带岩石圈地幔和软流圈为地震低速带,其根源可能与来自地幔底部的地幔热羽流有关。 相似文献
13.
E. P. Dubinin A. V. Kokhan D. E. Teterin A. L. Grokhol’sky E. S. Kurbatova N. M. Sushchevskaya 《Geotectonics》2016,50(1):35-53
Western, central, and eastern provinces are recognized in the Scotia Sea. They are distinguished by their bottom topography, geophysical characteristics, and crustal structure, which record their different origin and evolution. The western province is characterized by the oceanic crust that formed on the West Scotia Ridge, where active spreading may have ceased as a result of a collision between propagating rift and the structural barrier of the thick continental lithosphere of the Falkland Plateau. The central province is a series of blocks mainly composed of continental crust that subsided to various depths depending on the degree of extension in the course of rifting. These blocks are separated by local areas with oceanic crust formed due to the breakup of the continental crust and diffusive spreading. These areas are characterized by deep bottom and high values of Bouguer anomalies. The southern framework of the central province consists of subsided continental blocks and microcontinents divided by small spreading-type basins formed by lithospheric extension complicated by strike-slip faulting. The eastern province is composed of oceanic crust formed on the backarc spreading East Scotia Ridge. The results of density analysis, analog, and numerical simulations allowed us to explain some features of the structure and evolution of these provinces. The insight into tectonic structure of the provinces and their evolution allowed us to recognize several types of riftogenic basins differing in geodynamics, age, and geological and geophysical characteristics. 相似文献
14.
西南次海盆位于南海渐进式扩张的西南端,共轭陆缘结构和残留扩张脊保留完整,是研究南海深部结构和动力学机制的关键区域。前期研究发现,西南次海盆洋陆过渡带较窄、同扩张断层发育、地震反射莫霍面不清晰、具有慢速扩张等特征。然而,由于不同探测方法获取的地壳结构具有多解性,使得西南次海盆洋陆转换过程、慢速扩张洋壳结构与增生模式以及龙门海山岩石性质与地幔成因机制等基础科学问题尚存争议。为此我们建议在西南次海盆开展地质取样获取海山岩石样品,确定其年龄与性质,分析扩张后海山形成的深部动力过程;并对关键构造部署高精度的地震反射/折射联合探测,结合岩石物理分析,对西南次海盆进行构造成像和物质组成参数正反演,以实现壳幔尺度的地震学透视,为探索西南次海盆洋陆转换过程和洋壳增生模式提供重要的地球物理证据,以丰富和完善南海的动力学演化模式。 相似文献
15.
The Blovice accretionary complex, Bohemian Massif, hosts well-preserved basaltic blocks derived from an oceanic plate subducted beneath the northern active margin of Gondwana during late Neoproterozoic to early Cambrian. The major and trace element and Hf–Nd isotope systematics revealed two different suites, tholeiitic and alkaline, whose composition reflects different sources of melts within a back-arc basin setting. The former suite has composition similar to mid-ocean ridge basalts (MORB), yet with striking enrichment in large-ion lithophile elements (LILE) and Pb paralleled by depletion in Nb, in agreement with its derivation from depleted mantle fluxed by subduction-related fluids. In contrast, the latter suite has composition similar to ocean island basalts (OIB) with variable contribution of ancient, recycled crustal material. We argue that both suites represent volcanic members of Ocean Plate Stratigraphy (OPS) and indicate that the oceanic realm consumed by the Cadomian subduction was a complex mosaic of intra-oceanic subduction zones, volcanic island arcs, and back-arc basins with mantle plume impinging the spreading centre. Hence, the basalt geochemistry implies that two distinct domains of oceanic lithosphere may have existed off the Gondwana’s continental edge: an outboard domain, made up of old and less buoyant oceanic lithosphere (remnants of the Mirovoi Ocean surrounding former Rodinia?) that was steeply subducted and generated the back-arcs, and young, hot, and more buoyant oceanic lithosphere generated in the back-arcs and later involved in accretionary complexes as dismembered OPS. Perhaps the best recent analogy of this setting is the Izu Bonin–Mariana arc–Philippine Sea in the western Pacific. 相似文献
16.
The large hydrocarbon basin of South Caspian is filled with sediments reaching a thickness of 20–25 km. The sediments overlie a 10–18 km thick high-velocity basement which is often interpreted as oceanic crust. This interpretation is, however, inconsistent with rapid major subsidence in Pliocene-Pleistocene time and deposition of 10 km of sediments because the subsidence of crust produced in spreading ridges normally occurs at decreasing rates. Furthermore, filling a basin upon a 10–18 km thick oceanic crust would require twice less sediments. Subsidence as in the South Caspian, of ≥20 km, can be provided by phase change of gabbro to dense eclogite in a 25–30 km thick lower crust. Eclogites which are denser than the mantle and have nearly mantle P velocities but a chemistry of continental crust may occur beneath the Moho in the South Caspian where consolidated crust totals a thickness of 40–50 km. The high subsidence rates in the Pliocene-Pleistocene may be attributed to the effect of active fluids infiltrated from the asthenosphere to catalyze the gabbro-eclogite transition. Subsidence of this kind is typical of large petroleum provinces. According to some interpretations, historic seismicity with 30–70 km focal depths in a 100 km wide zone (beneath the Apsheron-Balkhan sill and north of it) has been associated with the initiation of subduction under the Middle Caspian. The consolidated lithosphere of deep continental sedimentary basins being denser than the asthenosphere, can, in principle, subduct into the latter, while the overlying sediments can be delaminated and folded. Yet, subduction in the South Caspian basin is incompatible with the only 5–10 km shortening of sediments in the Apsheron-Balkhan sill and south of it and with the patterns of earthquake foci that show no alignment like in a Benioff zone and have mostly extension mechanisms. 相似文献
17.
南海是中国唯一发育有洋壳的边缘海,是世界四大海洋油气聚集中心之一。油气勘探表明,南海的油气田分布在北部、西部和南部陆缘沉积盆地内,而大中型油气田集中分布在西部海域盆地中,自北而南有莺歌海—琼东南盆地、万安盆地、湄公盆地、曾母盆地和文莱—沙巴盆地,且以含气为主,含油次之。此外,这一区域深水区还存在多个潜在的大型含油气盆地。研究发现,南海的油气分布与深部岩石圈结构有密切关系。在构造上,南海的含油气盆地位于岩石圈块体边缘或之上,受控于大型岩石圈断裂的发育与演化。在油气富集的盆地中,莫霍面显著凸起,与盆地基底形成镜像,地壳厚度最薄处仅数千米厚,热流值明显较周围地区高,热岩石圈厚度大大减薄。地震层析成像结果反映,这些盆地深部发育一条规模宏大的北西向上地幔隆起带,自红河口向东南穿越南海西部海盆,一直延伸到婆罗州东北部地区,在宏观上控制了南海的油气分布与富集。 相似文献
18.
南海北部及其沿岸中、新生代壳幔相互作用与构造演化——纪念“陆缘扩张带”概念的倡导者陈国达教授 总被引：8，自引：5，他引：3
邹和平 《大地构造与成矿学》2005,29(1):78-86
新生代火山岩中的深源捕虏体资料反映,南海北部及其沿岸地区岩石圈地幔的主体由主量元素易熔组分相对饱满的、同位素组成类似MORB-OIB型的、高温型的二辉橄榄岩所组成;但在其顶部残留有古老的岩石圈地幔,它由主量元素易熔组分相对贫瘠的、同位素组成类似EM型的、较低温的方辉橄榄岩组成。在下地壳底部,分布着由晚中生代幔源岩浆分离结晶和堆晶的基性麻粒岩。由此提出了该区中、新生代壳 -幔或岩石圈 -软流圈相互作用与构造演化的简略模式: (1)印支期 -燕山早期为地壳岩石圈厚度增大的华夏型后地台活化造山带环境;(2)燕山晚期岩石圈快速减薄(如拆沉作用),造山带拉伸塌陷,地壳深处并发生广泛的底侵作用; (3)始新世 -渐新世软流圈再次上涌(如地幔柱的影响),岩石圈地幔发生底蚀减薄,地壳也因为下部层的塑性流展和上部层的张裂拉伸而减薄; (4)中新世以来,由于地幔热源在拉伸环境中被释放,壳幔发生冷却,部分软流圈地幔转化为“新生的”岩石圈地幔。研究进一步说明,南海北部陆缘扩张是该区大陆构造演化到大陆活化造山带后期,在深部壳 -幔的相互作用下,岩石圈所发生的垂向减薄和侧向伸展,既不同于弧后扩张,也不是受控于大西洋式的海底扩张。 相似文献
19.
四国海盆是位于菲律宾海板块内由岛弧张裂形成的弧后盆地,其深部地壳结构对认识伊豆小笠原岛弧的裂解和弧后盆地的扩张过程有重要的意义.在反射多道地震剖面和深部海底地震（OBS）探测剖面的约束下,结合磁异常条带数据,利用两条横穿四国海盆的重力测线数据对海盆的地壳物性结构反演,对比重力反演剖面与深部探测剖面地壳厚度和密度特征,得到更加精细的四国海盆地壳结构.研究结果显示,四国海盆洋壳厚度自西向东逐渐增厚,在残留扩张脊处莫霍面深度迅速增加.根据地壳密度和厚度将四国海盆分为:洋壳减薄区、洋壳增厚区、后扩张洋壳增生区,分别对应初始慢速张裂、单翼快速扩张、对称慢速扩张3期扩张活动.南北测线不同构造分区得到的扩张速率与由磁异常条带得到扩张速率相同;洋壳减薄区下地壳均有高密度体,与OBS剖面中下地壳高速体相对应,可能是由于洋壳慢速扩张过程中强烈拆离作用,地幔蛇纹石化导致. 相似文献
20.
Miao Dong Jian Zhang Xing Xu Jinwei Gao Taoran Song 《International Geology Review》2020,62(7-8):924-937
ABSTRACT The South China Sea (SCS) is an excellent site for studying the process of conjugate margin rifting, and the origin and evolution of oceanic basins. Compared with the well-defined northern margin of the SCS, the western and southern segments of the SCS margin have not been researched in significant detail. To investigate the regional structure of the southwestern SCS, a gravity model is constructed, along with the lithospheric thermal structure along a wide-angle seismic profile. The profile extends across the conjugate margins of the Southwest Sub-Basin (SWSB) of the SCS and is based on the latest multiple geophysical measurements (including heat flow and thermo-physical parameters). The results show that the average thicknesses of the crust and thermal lithosphere along the profile are about 15 km and 57 km, respectively. The overall amount of extension of continental crust and lithosphere is more than 200 km. Thermal structure of the lithosphere shows that the continental margins are in a warm thermal state. The southwest SCS is characterized by ultra-wide, thinned continental crust and lithosphere, high Moho heat flow, early syn-rift faulted basins, undeformed late syn-rifting, and high seismic velocities in the lower crust. These various pieces of evidence suggest that the break-up of the mantle lithosphere occurred before that of the continental crust favouring a depth-dependent extension of the southwestern SCS margin. 相似文献